Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium called a disc. Modern disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on a hub of a spindle motor for rotation at a constant high speed. Generally, each of the multiple discs in a disc drive has associated with it two heads (one adjacent the top surface of the disc, and another adjacent the bottom) for magnetically reading and writing data from and to the disc respectively. A typical disc drive has one or two discs. This usually means there are one to four heads in a disc drive carried by a set of actuator arms. Data is accessed by moving the heads from the inner to the outer part of the disc (and vice-versa) driven by an actuator assembly. Recording heads consist of two elements: a read element, or reader, and a write element, or writer. During a write operation, current is passed through the writer coils, generating a magnetic field that leaves a magnetic signature on the disc. During a read operation, an existing magnetic signature on the disc induces a current in the reader.
The writer element of a recording head is typically composed of a soft magnetic yoke encircled by coils and broken by a gap in the magnetic material, commonly referred to as the write gap. The portion of yoke containing the writer gap is exposed at the air bearing surface where it is referred to as the poles or pole tips. In various applications, including recording heads, it is desirable to construct features having a high aspect ratio. That is, the height (direction of film growth) of the feature, in this case a thin line, is much greater than its width (patterned dimension). For the purpose of recording heads in disc drives, the aspect ratio of the thin conductive line directly relates to the bit density of recorded data on the magnetizable medium. As the thickness of the conductive line decreases, and as its aspect ratio of height to width increases, the achievable bit density in recording increases. The storage capacity of a disc drive is therefore greater. It is accordingly desirable to form a high aspect ratio feature in the most efficient way.
One conventional high aspect ratio features such as conductive thin lines on wafers is as follows. First, a wafer is coated with photoresist. The photoresist material is selectively exposed to light and developed to form a photoresist pattern. In the developing process exposed areas of the photoresist are removed to create a pattern, specifically trenches, in which the feature will be formed. The resultant trench is then filled, typically by electroplating with the writer component material. The remaining photoresist is then removed, the feature is milled to form a notch in the shared pole, and an insulating material is deposited.
Using such a technique it is very difficult to form a trench within precise parameters and to control the angle of the walls of the trench. During the dissolving process, unexposed photoresist is consumed by the developing solution so the dimensions of the trench and the angle of its sidewalls are subject to inaccuracies. These parameters need to be carefully controlled if a high aspect ratio is to be achieved such as in order to create a thin, conductive line which can be used as a write pole for a disc drive head. As a result, the width of the trench becomes larger than was intended, and the desired high aspect ratio of a thin line is not achieved.
Accordingly there is a need to improve the conventional approach for a forming a high aspect ratio thin conductive line on a wafer.